Diagnosis of tumors and other diseased tissues has been greatly facilitated by the advent of nuclear medicine. For example, small amounts of radioisotopes, after being administered to a patient, concentrate differently in diseased and healthy tissues. The different concentrations of radiation, usually gamma rays, emitted by the healthy and diseased tissues are thus distinct and can be detected. The machines used to detect the radiation usually utilize a collimator to direct or transmit radiation to a scintillation crystal which changes the radiation to visible light during a scintillation. Photomultiplier tube or tubes detect the light and various means are used to locate the scintillations in the scintillator and, thus, indirectly find a tumor or other irregularity in the patient.
Radiation imaging devices include dynamic and static machines sometimes called scanners and cameras, respectively. Both machines have inherent limitations. The scanners move slowly over the patient and are considered to have better resolution and field uniformity. However, because scanners take a relatively long time to detect the radiation, they create some patient discomfort. A static imaging device, on the other hand, is relatively fast because it takes a single stationary picture. While faster than the scanner, it does not give as good resolution and field uniformity as the scanner. Resolution is used herein to mean the ability of the machine to distinguish two spaced points or line sources of radiation.
An example of a static imaging device is shown in Anger U.S. Pat. No. 3,011,057, the disclosure of which is incorporated by reference. The Anger device operates by spacing the photomultiplier tubes away from the scintillator so that the photomultiplier tubes view overlapping areas of the crystal. The spacing, however, causes the failure of some photons to be detected by the photomultiplier tubes and a loss in resolution results.
This invention seeks to overcome the disadvantage of both the scanner and static imaging device. Basically, this invention uses a plurality of photomultiplier tubes, not less than three and normally 19 or 37, which are placed in a hexagonal array substantially adjacent to the scintillator. In this location, the photomultiplier tubes receive the maximum number of photons but problems do occur. Spatial distortion and non-uniformity of the response of the scintillator result. Rather than back the photomultiplier tubes away from the crystal to avoid the problems, as was done in the device shown in the above-mentioned patent, spatial distortion and non-uniformity are corrected electronically. As a result of the combination of electronic distortion correction and maximum photon reception, resolution is vastly improved.